Multiple drum clamping unit

ABSTRACT

Multiple drum clamping attachment for lift trucks or other lifting devices, gripping and lifting one or a plurality of drums and depositing the drums in upright positions. Clamping jaws extend radially from the center of the attachment, each pair of which clamping jaws engages beneath and within the bead of a drum upon lowering movement of the attachment into engagement with the top of the drum and come into clamping engagement with the bead of the drum as elevated. The drums are maintained in generally vertical positions during lifting and lowering thereof by straightening abutments, extending generally radially from the center of the attachment on opposite sides of the clamping jaws. Each pair of straightening guides is adapted to engage the side of a drum on opposite sides of the clamping jaws and to extend downwardly along the drum beneath the center of gravity of the drum, to hold the drum from tilting during upward lifting movement of the drum.

Feb. 27, 1973 United States Patent [191.

Lund et al.

[ MULTIPLE DRUM CLAMPING UNIT [75] Inventors: Harold E. Land, Northbrook, 1.;

Primary Examiner-Harvey C. Hornsby Assistant ExaminerDouglas C. Bellis AttorneyCarlton Hill et al.

John F. E. Ericson, North Seminole, Fla.

[73] Assignee: Marvel Industries, Inc., Evanston,

[57] ABSTRACT Multiple drum clamping attachment for lift trucks or Fla.

other lifting devices, gripping and lifting one or a plu- [22] Filed: Nov. 18, 1971 [211 Appl. No.: 200,076

[52] US. Cl..................2l4/620, 214/655, 294/67 B,

upon lowering movement of the attachment into en- 294/81 R gagement with the top of the drum and come into [51] Int. 9/06 clamping engagement with the head of the drum as .294/93, 81 R, 67 BB, 67 BA, elevated. The drums are maintained in generally verti- -cal positions during lifting and lowering thereof by [58] Field of Search.....

,67 BC, 67 R; 214/620, 655

straightening abutments, extending generally radially from the center of the attachment on opposite sides of l the clamping jaws. Each pair of straightening guides is References C'ted adapted to engage the side of a drum on opposite sides UNITED STATES PATENTS 0f the clamping jaws and to extend downwardly along the drum beneath the center of gravity of the drum, to

3,338,616 8/1967 EfiCSOH...............................294/81 R the drum from tilting during upward move- Shramek.............................294/3l R ment of the drum- 10 Claims, 4 Drawing Figures lllllllllll I MULTIPLE DRUM CLAMPING UNIT FIELD OF THE INVENTION Attachment for lift trucks and the like, for lifting, transporting and stacking one or a series of drums.

BACKGROUND OF THE INVENTION A multiple drum handling device operated on principles similar to those of the present invention is shown and described in U.S. Pat. No. 3,338,616 which issued to John F. E. Ericson on Aug. 29, 1967 and is assigned to the assignee of the present invention. This drum handling device, while generally efficient in picking up and lifting a cluster of drums is not suitable to pick up a single drum or even two or three drums, because the drums as clamped and lifted above the ground tilt to an undesirable extent and, if not manually held upright when set on the ground, many times fall over on their sides. This drum handling device, therefore, is not satisfactory for lifting, transporting and setting drums in upright positions for storage or use, and cannot be used for stacking drums one on top of another unless an entire cluster of four drums is lifted and stacked at one time.

The present invention, therefore, improves upon the prior invention disclosed in U.S. Pat. No. 3,338,616 in that the clamping unit is so arranged as to enable one, two, three or four drums to be picked up at a time and to hold the drums in generally vertical positions, to enable the drums to be set down on the ground or stacked without tilting, and without the aid of a man to prevent tilting thereof, as has heretofore been necessary in the prior drum handling devices.

The advantages of the present invention are that the device may grip and lift one, two, three or four drums of a seriesof drums and set the drums on the ground or stack one on top of the other in upright positions without manual aid to prevent tipping over of the drums as set down.

Still another advantage of the invention is to provide a multiple drum clamping unit gripping beneath and within the bead of one drum or the beads of a series of drums, and maintaining the drums in generally upright positions during lifting and lowering thereof.

A further advantage of the invention is in the simplified arrangement of clamping unit, clamping beneath and within the bead of a single drum or a series of drums and holding the drum or drums in generally vertical positions during lifting and lowering movement thereof.

Other objects, features and advantages of the invention will be readily apparent from the following description of a preferred embodiment thereof, taken in conjunction with the accompanying drawings, although variations and modifications may be effected without departing from the spirit and scope of the novel concepts of the disclosure.

DESCRIPTION OF THE DRAWINGS FIG. 1 is a perspective view of the device, showing the device in the process of being lowered by the forks of a fork lift truck, to grip and pick up a pair of drums resting on the ground, with the drums shown in phantom.

FIG. 2 is a partial fragmentary vertical sectional view taken through the drum clamping unit, and showing the clamping jaw arrangement and support and actuating means therefor.

FIG. 3 is a transverse sectional view showing the pawl and ratchet holding means for the actuator frame for the clamping jaws; and

FIG. 4 is a partial fragmentary vertical sectional view showing the support for the spider on the housing attachment for the lift truck, and generally illustrating the centering means therefor.

DESCRIPTION OF PREFERRED EMBODIMENT OF INVENTION In FIG. 1 of the drawings a generally horizontal housing 10 opening toward the ground is shown as having opposite fork openings 11 extending along each side thereof for receiving forks 12 of a fork lift truck 13. The forks 12 and fork lift truck 13 are only shown herein in phantom in a fragmentary form since the forks and lift truck may be of any conventional construction and are no part of the present invention. The housing 10 forms a suspension means for a multiple drum clamping unit 15 suspended from said housing for lateral movement with respect thereto to enable the clamping unit to center itself between a cluster of drums and yieldably centered with respect to said housing as the drums are set on the ground and released. It should be understood, however, that where it is desired to use the clamping unit as an attachment for a crane,

I the housing 10 need not necessarily be used.

The clamping unit 15 includes a spider 16 of the same general cross-like form as a spider of the aforementioned U.S. Pat. No. 3,338,616. The spider 16 has a square central portion in the general form of .an open rectangle and has parallel spaced side rails 17 extending radially of the center of said central portion and spaced apart and forming pivotal mountings adjacent the inner ends thereof for cantilever beams 19. The cantilever beams are of a generally downwardly opening U-shaped form and have casings 20 for respective upper and lower clamping jaws 21 and 22 disposed therebetween and depending therefrom as will hereinafter more clearly appear as this specification proceeds. The rectangular central open portion of the spider 16 is formed by connected parallel spaced plates 23 extending downwardly for a substantial distance and receiving the jaw casings 20 in the space therebetween. The guide plates 23 extend outwardly of and along each corner of the rectangular open portion of the spider, and the inner sides thereof extend along opposite sides of the casings 20. Opposite sides 24 of said guide plates from the clamping jaws are at right angles to the next adjacent guide plate at the corner of the frame and form right angled elongated recesses for abutment and guide members 25 of such a length as to extend beneath the center of gravity of the drum to be picked up, as a plate 26 rests on top of a drum and the lower and upper clamping jaws 21 and 22 are in position to engage beneath and within the bead of a drum.

The rectangular open central portion of the spider 16 is closed at its top by an end cap 27 extending upwardly therefrom within a central open portion 29 of a top plate 30 of the housing 10. A retainer plate 31 extends over the top of the plate 30 of the housing 10 beyond manipulating the lift truck 13 to center the unit.

The spider 16 is yieldably centered with respect to the top plate 30 as by tension springs 33. As shown in FIG. 4, the tension springs 33 are hooked at their lower ends to hooks 35, extending outwardly of top gussets 36 of a series of vertically spaced gussets. Said gussets are welded or otherwise secured to the right angled portions 24 of the adjacent guide plates 23, and form mountings for hinge pins 37 for the abutment and guide members 25.

The centering springs 33 extend angularly upwardly of the hooks 35 through the plate 26, and are booked at their upper ends to diagonal pins 39, extending diagonally from the bottom of the plate 30 to the side and end walls of the housing to bias the spider 16 in centered relation with respect to said housing.

A plate 26 is provided on each side of each jaw casing and extends from the top of the right angled portion 24. Said plates may be in the form of ring segments connected and suspended from the side rails 17 as by rods 40.

An actuator frame 41 fits within the side rails 17 of the spider 16, and like the spider 16, is of a generally cross-like form and has a rectangular central open portion 45 fitting within the open portion of the spider. The actuator frame 41 is guided for vertical movement with respect to said spider under the control of a holding pawl 53 and a release pawl 57. The actuator frame has pairs of parallel arms 43 disposed within the side rails 17 and extending outwardly of the rectangular central open portion 45. A vertical guide sleeve 46 extends along the center of said rectangular central open portion 45. The guide sleeve 46 may be mounted at its upper end on a plate 47 extending across the top of said central open portion. Said sleeve extends downwardly from said plate through a vertically spaced latch plate 48 and beneath said latch plate as shown in FIGS. 2 and 3. The guide sleeve 46 is guided for movement along a vertical rod 49 secured at its upper end to the cap 27, and at its lower end to a cross frame member 50 extending across the rectangular hollow interior portion of the spider 16 and secured to the plates 23. The sleeve 46, guided for movement along the rod 49, thus maintains the actuator frame in centered relation with respect to the spider l6 and holds said actuator frame from tilting or skewing relative to said spider.

The parallel arms 43 of the spider 16 have downwardly facing abutment surfaces 51 extending along their outer end portions and depending from the ring sectors 26, when the clamping unit is suspended above a drum and positioned to come into engagement with the top of a drum to be picked up during lowering movement of the clamping unit. This will cam the latch 43 in a released position and move the actuator frame 41 toward the end cap 27, to position the casing and clamping jaws 21 and 22 into position to engage beneath and within the bead of a barrel, and to clamp the bead and raise the barrel upon upward lifting movement of the spider 16, as will hereinafter more clearly appear as this specification proceeds.

The actuator frame 41 is latched in the position shown in FIGS. 2 and 3 by the latch 53 having latching engagement with a latch plate 48. The latch 53 is pivoted at its upper end to a block 55 suitably secured to and depending from the end cap 27. A pivot pin 56 forms a pivotal mounting for said latch. The pivot pin 56 also forms a pivotal mounting for the pawl 57. The pawl 57 serves to advance a ratchet 59 in a clockwise direction upon movement of the actuator frame 41 toward the block 55. The ratchet 59 is suitably secured to a sleeve 60 rotatably mounted on a shaft 61 carried by the actuator frame 41 at its ends and extending across the rectangular hollow central portion of said actuator frame 41. A release cam 62 is also carried by the sleeve 60 and is rotated by the ratchet 59, as the actuator frame 41 moves toward the block 55.

The release cam 62 is shown as being of a generally star-like form which in the position of said cam shown in FIG. 3 accommodates the holding pawl to lockingly engage the latch plate 48 under the bias of a spring (not shown) engaging the upper end portion of the holding pawl in offset relation with respect to the shaft 56. A similar spring 63 biases a tooth 64 of the pawl 57 into engagement with the ratchet 59.

A spring biased pawl 65 is provided to hold the cam 62 in position to accommodate the latch lever 53 to engage the keeper plate 48 or to hold said latch lever 53 free from the latch plate 48. This is attained by engagement of a tooth of the cam 62 with said latch lever in a manner similar to that shown inPat. No. 3,338,616, so not herein shown or described further.

The jaw casing 20 is yieldably biased in the upright,

position shown in FIG. 2 by a tension spring 67 connected between the lower outerend portion of said jaw casing and a top plate 68 of the actuator lever. The cantilever arm 19 is also biased in an upright position by a torsion spring 70, encircling a pivot pin 71 for said cantilever arm, and engaging a pin 72 extending inwardly of a side rail 17 at one end and a pin 73 extending inwardly of said cantilever arm at its opposite end.

The jaw casing 20 is pivotally supported on the cantilever arm 19 intermediate the ends of said arm as by a pivot pin 75. A control lever 76 is also pivoted on the pivot pin within the jaw casing 20, and extends angularly inwardly and downwardly along said jaw casing, and has a downwardly opening slot 77 at its lower end slidably engaging a pin '79 on a control link 80. The control link 80 in turn is pivotally connected with an upper clamping jaw 22 outwardly of the pivotal axis of said clamping jaw as by a pivot pin 81.Said control link 80 extends downwardly along one side of the lower clamping jaw 21 and is pivotally connected thereto outwardly of the pivot for said jaw, as by a pivot pin 82. The pivot for the upper clamping jaw 22 is in the form of a pivot pin 83 spaced inwardly of the pivot pin 81 and extending across the jaw casing. A pivot pin 85 extends across the jaw casing 20, adjacent the lower end portion thereof, and extends within an arcuate slot formed in the jaw 21 adjacent its lower end portion, and forms a pivot for said lower jaw accommodating slidable movement along the pin 85, during a gripping operation. A tension spring 86 is connected between a lug 87 extending angularly upwardly and inwardly of the jaw 21 adjacent the pivot thereof and a pin 88 on the control link 80, and biases the clamping jaw 21 into the outwardly extended position shown in FIG. 2.

The control lever 76 has an upwardly opening slot 89 therein, adjacent the upper lower end portion thereof and registrable with a pin 90 on the end of a lever 91. The lever is pivoted for movement about the axis of a pivot pin 92 and biased in an angular downward and outward direction as by a torsion spring 93. The pin 90 extends beyond opposite sides of the jaw casing 20 through arcuate slots 95 in said jaw casing, extending in a generally upright direction, and is biased into engagement with camming faces 96 extending along the top surfaces of the parallel arms 43 of the actuator frame 41, by the torsion spring 93.

As the clamping unit is moved downwardly into engagement with a drum with the clamping jaws 21 and 22 in the position shown in FIG. 1, the jaw 21 will first engage the bead or chime of the drum to be picked up then will move inwardly into position to engage the chime of the drum. The abutment surface 51 of the actuator frame 41 will also come into engagement with the top of the drum, and move the actuator frame 41 upwardly to release the latch 53 from the keeper plate 48. At this time, the tooth 64 of the pawl 57 will advance the ratchet 59 a distance of one tooth and move a tooth of the cam wheel 62 into position to hold the latch 53 in a released position with respect to the latch plate 48. During this movement, the pin 90 will be cammed by the camming surface 96 in a direction to position the upper jaw 22 to engage within the bead of the drum as the lower jaw 21 engages the bead or chime of the drum and to clamp the jaws to the bead or chime of the drum and raise the drum as the entire unit is raised. As the clamping unit is moving upwardly, a bead 21a on the under advance end of the jaw 21, will keep the leading end of the jaw from the flange of a fiber drum to prevent damage to the flange, and will position the jaw to engage the bead or chime of the drum, as said jaw moves upwardly.

Except for structural details improving the efficiency of gripping and the reversal of the gripping effect of the jaws to attain greater gripping power the clamping unit so far operates on the same general principles as that disclosed in the Ericson U.S. Pat. No. 3,338,616. The detailed structure just described, however, places many refinements in the gripping device, increasing the holding power of the unit and cooperating with the straightening guide structures 25 to enable one, two, three or four drums to be lifted, and then set down or stacked on their ends without tipping over.

The abutment and guide structures 25 each include a vane 94 having a pair of vertically spaced and aligned sleeves 99 extending along the inner sides thereof between the upper and lower sets of gussets 37 and 38 and adapted to receive the hinge pins 37. The pins 37 each have a head at the upper end thereof and are drilled at the lower end thereof, beneath the gusset 38 to accommodate the insertion of a cotter pin and the like, to lock the hinge pin in position. 97

Each vane 97 also has socket members 100 extending inwardly from opposite sides thereof between the gussets 36 and 38 and at right angles with respect to each other. The socket members 100 form sockets for compression springs 101 engaging the outwardly facing right angled faces 24 of the plates 23 and biasing the respective vane 29 in centered relation with respect to said faces, but accommodating yieldable pivotal movement of said vanes about the axis of the pivot pins 37, as the clamping unit is lowered between a series of drums or along the outer side of a single drum. Each vane 97 has a buffer member 103 extending downwardly along the outer side thereof, and angularly inwardly along the bottom thereof, and terminating beneath the bottom of the vane 97 and guide portion of the spider 16. The buffer member 103 may be in the form of a pipe or tube, having a slot extending vertically therealong to fit along the vane 97. Said buffer member may be welded or otherwise secured to said vane. The four buffer members 103, converging towards each other beneath the vanes 97 and plates 24, thus center the unit with a single drum or a plurality of drums as moving downwardly therealong.

In lifting one, two or three drums and particularly a single drum, as shown in FIG. 1, the clamping unit is lowered with the abutment and buffer guides extending along the drum in circumferentially spaced relation, and centering the spider and clamping jaws with respect to a drum, to engage the head of a drum as lowered to release the actuator frame from the spider. The abutment and buffer guides extending downwardly beneath the center of gravity of the drum, are thus biased into engagement with the drum by the springs 101 and the lifting force of the clamping jaws 21 and 22 is sufficient to maintain the drum in engagement with said guides, which in turn hold the drum straight as lifted and lowered, so it may be set on the floor or on a pallet without any tendency to tip over, and may readily be stacked on top of other drums.

We claim as our invention:

1. In a multiple drum clamping unit of a type adapted as an attachment for a lift truck and the like, to clamp and lift one or more of a series of drums,

a spider adapted to be raised and lowered toward and from a drum to be picked up,

means suspending said spider and accommodating said spider to align itself with respect to a drum as lowered,

said spider having a central depending guide portion having outwardly facing right angled walls at each corner of said guide portion and parallel walls at opposite sides of said guide portion and of a greater length than the distance from the top of a drum to be picked up to the center of gravity of the drum,

jaw casings carried by said spider between the parallel walls of said right angled wall portions and each having an upper and a lower clamping jaw pivotally mounted therein and extending outwardly therefrom, for engaging the bead of a drum,

a control arm pivotally mounted within said casing and having control connection with said clamping jaws for extending and retracting said clamping jaws relative to said casing,

a cantilever arm for each casing, yieldably biased in an upward position relative to said spider and movably supporting each casing and the clamping jaws carried thereby on said spider,

an actuator frame movably mounted on said spider and having control connection with said clamping jaws through said control arm and extending said jaws in position to come into gripping engagement with the head of a drum upon engagement of said actuator frame with the top of a drum, and

abutment and guide means carried by said spider between the right angled wall portions thereof, for lateral movement the to said wall portions,

said abutment and guide means including generally radially extending vanes extending along said right angled wall portions beneath he bottoms thereof and longer in vertical dimensions than the distance from the top of a drum to the center of gravity thereof when said actuator frame is in engagement with the top of a drum,

said vanes having buffer members extending along the outer ends thereof for the entire height thereof, for engagement with the drum at circumferentially spaced points spaced equally from the opposite sides of said clamping jaws and centering said spider relative to the drum and retaining the drum in an upright position upon upward lifting movement of said spider and clamping jaws.

2. The multiple drum clamping unit of claim 1,

wherein the vanes are vertically pivoted to said guide portion of said spider between the right angled wall portions thereof.

3. The multiple drum clamping unit of claim 2,

wherein spring means bias the vanes into centered relation relative to the right angled wall portions of said central guide portion of said spider.

4. The multiple drum clamping unit of claim 3,

wherein the buffer members are generally tubular in form and converge towards each other beneath said vanes.

5. The multiple drum clamping unit of claim 2,

wherein said spider limits vertical movement of said actuator frame, and

wherein said actuator frame has abutment surfaces extending beneath said spider as said spider is spaced from the top of a drum and engageable with the top of a drum, to move said spider upwardly relative to said frame upon lowering movement of said spider into engagement with the top of the drum, and positioning said clamping jaws in position to engage the head of a drum.

6. The multiple drum clamping unit of claim 5,

wherein a control connection is provided between the actuator frame and spider and includes a generally vertically extending slot in said jaw casmg,

a pin extending through said slot and beyond at least one side of said casing,

an arm pivoted to said casing and forming a mounting for said pin,

spring means biasing-said arm downwardly relative to said slot,

a control connection between said pin and said control arm, and

wherein said actuator frame has an upwardly facing camming surface camming said pin along said slot upon movement of said actuator frame upwardly toward said spider, as said actuator frame engages the bead of a drum.

7. The multiple drum clamping unit of claim 6, wherein the control arm is pivoted to said casing for movement about the axis of pivotal movement of said casing to said cantilever arm, and

wherein a control link has pivotal control connection with said upper and lower jaws, and a control connection is provided between said control arm and said control link.

8. The multiple drum clamping unit of claim 7, in-

cluding spring means connected between said control link and the lower of said clamping jaws and biasing the lower of said clamping jaws to move outwardly relative to said casing.

9. The multiple drum ciamping unit of claim 8,

wherein a pin is carried by said casing and extends transversely thereof and a slot in said lower clamping jaw accommodates pivotal and retractable movement of said lower clamping jaw relative to said pin and casing.

10. The multiple drum clamping unit of claim 9,

wherein the lower of said clamping jaws has a bead engaging leading end and a bead extending thereacross beneath said leading end and engaging the bead of a drum upon lowering movement of said clamping unit, and positioning said bead engaging leading end of said jaw away from the drum to come into engagement with the bead of the drum upon upward movement of the clamping unit.

* it l l 

1. In a multiple drum clamping unit oF a type adapted as an attachment for a lift truck and the like, to clamp and lift one or more of a series of drums, a spider adapted to be raised and lowered toward and from a drum to be picked up, means suspending said spider and accommodating said spider to align itself with respect to a drum as lowered, said spider having a central depending guide portion having outwardly facing right angled walls at each corner of said guide portion and parallel walls at opposite sides of said guide portion and of a greater length than the distance from the top of a drum to be picked up to the center of gravity of the drum, jaw casings carried by said spider between the parallel walls of said right angled wall portions and each having an upper and a lower clamping jaw pivotally mounted therein and extending outwardly therefrom, for engaging the bead of a drum, a control arm pivotally mounted within said casing and having control connection with said clamping jaws for extending and retracting said clamping jaws relative to said casing, a cantilever arm for each casing, yieldably biased in an upward position relative to said spider and movably supporting each casing and the clamping jaws carried thereby on said spider, an actuator frame movably mounted on said spider and having control connection with said clamping jaws through said control arm and extending said jaws in position to come into gripping engagement with the bead of a drum upon engagement of said actuator frame with the top of a drum, and abutment and guide means carried by said spider between the right angled wall portions thereof, for lateral movement the to said wall portions, said abutment and guide means including generally radially extending vanes extending along said right angled wall portions beneath he bottoms thereof and longer in vertical dimensions than the distance from the top of a drum to the center of gravity thereof when said actuator frame is in engagement with the top of a drum, said vanes having buffer members extending along the outer ends thereof for the entire height thereof, for engagement with the drum at circumferentially spaced points spaced equally from the opposite sides of said clamping jaws and centering said spider relative to the drum and retaining the drum in an upright position upon upward lifting movement of said spider and clamping jaws.
 2. The multiple drum clamping unit of claim 1, wherein the vanes are vertically pivoted to said guide portion of said spider between the right angled wall portions thereof.
 3. The multiple drum clamping unit of claim 2, wherein spring means bias the vanes into centered relation relative to the right angled wall portions of said central guide portion of said spider.
 4. The multiple drum clamping unit of claim 3, wherein the buffer members are generally tubular in form and converge towards each other beneath said vanes.
 5. The multiple drum clamping unit of claim 2, wherein said spider limits vertical movement of said actuator frame, and wherein said actuator frame has abutment surfaces extending beneath said spider as said spider is spaced from the top of a drum and engageable with the top of a drum, to move said spider upwardly relative to said frame upon lowering movement of said spider into engagement with the top of the drum, and positioning said clamping jaws in position to engage the bead of a drum.
 6. The multiple drum clamping unit of claim 5, wherein a control connection is provided between the actuator frame and spider and includes a generally vertically extending slot in said jaw casing, a pin extending through said slot and beyond at least one side of said casing, an arm pivoted to said casing and forming a mounting for said pin, spring means biasing said arm downwardly relative to said slot, a control connection between said pin and said control arm, and wherein said actuator frame has an upwardly facing camming surface camming said Pin along said slot upon movement of said actuator frame upwardly toward said spider, as said actuator frame engages the bead of a drum.
 7. The multiple drum clamping unit of claim 6, wherein the control arm is pivoted to said casing for movement about the axis of pivotal movement of said casing to said cantilever arm, and wherein a control link has pivotal control connection with said upper and lower jaws, and a control connection is provided between said control arm and said control link.
 8. The multiple drum clamping unit of claim 7, including spring means connected between said control link and the lower of said clamping jaws and biasing the lower of said clamping jaws to move outwardly relative to said casing.
 9. The multiple drum clamping unit of claim 8, wherein a pin is carried by said casing and extends transversely thereof and a slot in said lower clamping jaw accommodates pivotal and retractable movement of said lower clamping jaw relative to said pin and casing.
 10. The multiple drum clamping unit of claim 9, wherein the lower of said clamping jaws has a bead engaging leading end and a bead extending thereacross beneath said leading end and engaging the bead of a drum upon lowering movement of said clamping unit, and positioning said bead engaging leading end of said jaw away from the drum to come into engagement with the bead of the drum upon upward movement of the clamping unit. 